US20230256534A1 - Resistance spot welding method and method of manufacturing weld joint - Google Patents

Resistance spot welding method and method of manufacturing weld joint Download PDF

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Publication number
US20230256534A1
US20230256534A1 US18/005,057 US202118005057A US2023256534A1 US 20230256534 A1 US20230256534 A1 US 20230256534A1 US 202118005057 A US202118005057 A US 202118005057A US 2023256534 A1 US2023256534 A1 US 2023256534A1
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Prior art keywords
nugget
steel sheets
spot welding
steel sheet
resistance spot
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Satoshi Maeda
Kazuki ENDOH
Yuki Toji
Nao Kawabe
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JFE Steel Corp
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JFE Steel Corp
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Assigned to JFE STEEL CORPORATION reassignment JFE STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: Endoh, Kazuki, KAWABE, Nao, MAEDA, SATOSHI, TOJI, YUKI
Publication of US20230256534A1 publication Critical patent/US20230256534A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/10—Spot welding; Stitch welding
    • B23K11/11—Spot welding
    • B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
    • B23K11/163—Welding of coated materials
    • B23K11/166—Welding of coated materials of galvanized or tinned materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/36—Auxiliary equipment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
    • B23K31/02—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to soldering or welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
    • B23K31/12—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to investigating the properties, e.g. the weldability, of materials
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • C21D3/06—Extraction of hydrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/18—Sheet panels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/34—Coated articles, e.g. plated or painted; Surface treated articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/02—Iron or ferrous alloys
    • B23K2103/04—Steel or steel alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals

Definitions

  • This disclosure relates to a resistance spot welding method suitable for manufacturing a weld joint that exhibits excellent delayed fracture resistance, and a method of manufacturing a weld joint using the resistance spot welding method.
  • This disclosure is particularly suitable for resistance spot welding of high strength steel sheets. Further, this disclosure is particularly suitable for use in the manufacturing process of automotive parts for automobiles and the like and in the assembly process of automotive bodies.
  • Resistance spot welding is widely used for the processing of the appearance of vehicles such as automobiles because the appearance is good after the welding.
  • Resistance spot welding is one of the techniques to join metals by applying pressure to the metals.
  • resistance spot welding is a technique of joining metals by applying electrodes from both sides of two or more metals (e.g., steel sheets) to be joined, gradually melting the metals by current while applying moderate pressure, and then cooling the metals to solidify the melted portion.
  • a heat-affected zone (HAZ) which is formed at and around a portion where metals are joined and which is melted by joining, is called a nugget. Further, a portion joined via a nugget is called a weld joint.
  • Delayed fracture is a phenomenon in which the metal suddenly fractures after a period of time has elapsed since the welding or other processing, even though the stress applied to the metal is below its yield stress.
  • high strength steel sheets are sometimes used as steel sheets for automobiles and other vehicles to improve the crashworthiness by strengthening the automotive body.
  • a high strength steel sheet is a steel sheet to which not only a large amount of C but also various alloying elements are added to increase the strength, but it has susceptibility to hydrogen embrittlement. Therefore, the delayed fracture described above is a particularly serious problem in resistance spot welding of high strength steel sheets.
  • JP 6194765 B proposes a technique of applying welding current at a certain electrode force, then applying subsequent-current at an electrode force higher than the certain electrode force, and further holding the electrodes, to reduce tensile residual stress in a welded portion and improve delayed fracture resistance.
  • PTL 1 describes that, after holding the electrodes, further performing “heat treatment after welding” at 120° C. to 220° C. for 100 seconds to 6000 seconds reduces the amount of hydrogen that has penetrated into the welded portion, which is advantageous in preventing delayed fracture.
  • the technique of PTL 1 focuses solely on reducing tensile residual stress by optimizing the electrode force and current pattern to prevent delayed fracture, and there is room for further improvement in hydrogen embrittlement of a steel sheet.
  • the technique of PTL 1 has a problem that, because the welded portion cools rapidly during the non-current cooling time provided between the welding current and the subsequent-current, a large amount of hydrogen remains without diffusing to the outside of the nugget, which increases the amount of residual hydrogen inside the nugget. As a result, there is a concern that it is difficult to suppress delayed fracture caused by the residual hydrogen.
  • a resistance spot welding method comprising:
  • the “nugget” is usually formed on the side of the overlapping surfaces of the steel sheets (see reference signs 12 and 22 in FIGS. 1 and 3 ) and cannot be directly confirmed from the surface of the steel sheet after resistance spot welding (see reference signs 11 and 21 in FIGS. 1 and 3 ). However, it can be confirmed that a “nugget” has been formed from a welding trace caused on the surface of the steel sheet by the welding. Further, “irradiating the nugget with sound waves” can be performed by, for example, irradiating a portion of the surface of the steel sheet where the welding trace can be confirmed (hereinafter, also referred to as “nugget-equivalent surface”, and see reference sign 6 in FIG. 2 and reference signs 13 and 23 in FIG. 3 ) with sound waves.
  • the “frequency” and the “sound pressure level” can be measured, for example, according to the methods described below.
  • a method of manufacturing a weld joint comprising:
  • the resistance spot welding method of the present disclosure even when steel sheets are joined, the problem of delayed fracture can be satisfactorily avoided without changes in the material properties of the steel sheet due to microstructural changes caused by heat treatment. According to the method of manufacturing a weld joint of the present disclosure, it is possible to easily obtain a weld joint that exhibits excellent delayed fracture resistance.
  • FIG. 1 schematically illustrates forming a nugget to join steel sheets according to one embodiment of the present disclosure
  • FIG. 2 is a plan view of steel sheets after joining according to one embodiment of the present disclosure from one surface side;
  • FIG. 3 schematically illustrates how a nugget-equivalent surface is irradiated with sound waves after steel sheets are joined according to one embodiment of the present disclosure.
  • two or more overlapped steel sheets such as steel sheets 1 and 2
  • a pair of welding electrodes 4 and 5 current is applied to the steel sheets while pressing the steel sheets
  • a nugget 3 is formed on the side of the overlapping surfaces (overlapping portions) 12 and 22 of the steel sheets to join the steel sheets, and then the nugget 3 (for example, at least one of the nugget-equivalent surfaces 13 and 23 ) is irradiated with sound waves at a predetermined frequency and a predetermined sound pressure level.
  • the problem of delayed fracture of the spot-welded portion can be avoided in a good and simple manner, without any change in material properties due to microstructural changes caused by heat treatment, by efficiently releasing hydrogen that accumulates mainly in the nugget to the outside of the steel sheet.
  • the method of manufacturing a weld joint of the present disclosure also has the same features as the resistance spot welding method of the present disclosure described above. According to the method of manufacturing a weld joint of the present disclosure, a weld joint having excellent delayed fracture resistance can be easily obtained.
  • a steel sheet portion including the nugget By irradiating a nugget formed in joining with sound waves under predetermined conditions, a steel sheet portion including the nugget is forcibly vibrated. Due to bending deformation caused by this forced vibration, the lattice spacing of the steel sheet portion including the nugget repeats expansion (tension) and contraction (compression) in the thickness direction. Hydrogen in the steel where the lattice spacing is expanded is induced to diffuse to the tensile side where the potential energy is lower, so that the expansion and contraction of the lattice spacing promotes the diffusion of hydrogen, and a hydrogen diffusion path connecting the inside and the surface of the steel sheet is forcibly formed.
  • Hydrogen for which a diffusion path has been intentionally formed, escapes through the surface to the outside of the steel sheet, where it is more energetically advantageous, at the time when the lattice spacing in the vicinity of the steel sheet surface is expanded.
  • the sound wave irradiation on the joined steel sheets under the predetermined conditions sufficiently and efficiently reduces the hydrogen that accumulates in the steel, especially in the nugget that is the area of tensile residual stress, thereby suppressing delayed fracture of a weld joint in a good and simple manner.
  • the resistance spot welding method of the present disclosure in detail according to several embodiments, but the resistance spot welding method of the present disclosure is not limited to these embodiments. Further, the method of manufacturing a weld joint of the present disclosure has the same features as those detailed for the resistance spot welding method of the present disclosure, and the method of manufacturing a weld joint of the present disclosure is not limited to the embodiments described below.
  • the resistance spot welding method of the present disclosure allows hydrogen to escape efficiently from the nugget after joining the steel sheets. Therefore, the processes up to joining a plurality of steel sheets are not particularly limited and may be performed under general conditions for resistance spot welding.
  • General current conditions for resistance spot welding include, for example, a current of 1 kA to 15 kA, a current time of 100 ms to 2000 ms, and an electrode force of 0.5 kN to 10 kN.
  • a pair of welding electrodes 4 and 5 are pressed against the surfaces 11 and 21 of two overlapped steel sheets 1 and 2 and current is applied.
  • the portions of the overlapping surfaces 12 and 22 of the steel sheets on which current is applied are once melt due to resistance heating and then solidified to form a nugget 3 .
  • the steel sheets 1 and 2 are joined via the solid nugget 3 .
  • This nugget 3 usually does not appear directly on the surfaces 11 and 21 of the joined steel sheets.
  • burn traces and/or dent welding traces are formed as resistance spot welding points 6 at the locations where the welding electrodes 4 and 5 are pressed.
  • the nugget 3 exists inside the thickness direction of the resistance spot welding point 6 , and the resistance spot welding point 6 can be treated as a “nugget-equivalent surface” in the process of irradiation of sound waves described below.
  • the steel sheet used in the resistance spot welding method of the present disclosure is not particularly limited, but it is preferably a high strength steel sheet.
  • the tensile strength of at least one of the steel sheets to be joined is preferably 780 MPa or more.
  • the tensile strength is more preferably 1000 MPa or more.
  • the tensile strength is still more preferably 1300 MPa or more. It is further preferably that all of the steel sheets to be joined have the tensile strength described above.
  • the tensile strength of the steel sheet to be joined is less than 780 MPa, the degree of tensile residual stress caused in the nugget by resistance spot welding is small. In this case, delayed fracture hardly occurs in a resulting weld joint.
  • the strength of the steel sheet to be joined increases as described above, hydrogen is more likely to be formed in the nugget or to penetrate into the nugget due to resistance spot welding, and delayed fracture is more likely to occur in the weld joint. Therefore, the effect of improving the delayed fracture resistance of the weld joint by irradiation of sound waves is improved.
  • the tensile strength of the steel sheet is not particularly limited, it may be 3000 MPa or less.
  • the chemical composition of the steel sheet is not particularly limited, but it is preferable that the chemical composition be such that the steel sheet can be a high strength steel sheet as described above.
  • Preferred examples of the high strength steel sheet chemical composition include a steel sheet having a C content of 0.05 mass % or more and 0.50 mass % or less.
  • the resistance spot welding method of the present disclosure performs non-contact irradiation of sound waves and is a welding method that is not affected by the surface conditions of the steel sheet, any surface treatment such as coating can be performed for the purpose of imparting desired properties to the steel sheet.
  • the coating may be formed by any of organic coating, inorganic coating, and metal coating, and the coating may be performed according to known techniques. Above all, from the viewpoint of preventing rust and corrosion, the coating is preferably a hot-dip galvanized (GI) coating or a galvannealed (GA) coating.
  • GI hot-dip galvanized
  • GA galvannealed
  • the nugget e.g., at least one of the nugget-equivalent surfaces
  • the sound waves should have a frequency of 10 Hz or more and 100000 Hz or less and the sound pressure level on the surface of the steel sheet should be 30 dB or more.
  • the sound wave irradiation in the present disclosure is performed without contacting the steel sheet.
  • the “frequency” refers to the frequency (Hz) on the sound wave output side set in any sound wave irradiator or the like.
  • the “sound pressure level” refers to the sound pressure level (dB) received by a portion of the surface of the steel sheet irradiated with the sound waves, where specific examples include the nugget-equivalent surface, and it can be measured using an arbitrary sound level meter placed at the location of the portion (nugget-equivalent surface) irradiated with the sound waves.
  • the frequency of the sound waves to be applied is preferably 100 Hz or higher. It is more preferably 500 Hz or higher. It is still more preferably 3000 Hz or higher. As the frequency of the sound waves to be applied increases, the bending deformation on the steel sheet becomes large.
  • the frequency of the sound waves to be applied should be 100 kHz or less. It is preferably 80 kHz or less. It is more preferably 50 kHz or less.
  • the sound pressure level of the sound waves to be applied is preferably 60 dB or more. It is more preferably 70 dB or more. As the sound pressure level of the sound waves to be applied increases, the steel sheet is further vibrated, and the residual hydrogen is further released from the steel, especially from the nugget, thereby further suppressing delayed fracture.
  • the sound pressure level of the sound waves to be applied is usually 140 dB or less.
  • the sound pressure level received by the nugget-equivalent surface can be controlled, for example, by changing the output of the sound wave irradiator or by appropriately adjusting the distance between the nugget-equivalent surface and the sound wave irradiator.
  • the time for irradiation of sound waves is preferably 1 second or longer. It is more preferably 5 seconds or longer. It is still more preferably 10 seconds or longer.
  • the time for irradiation of sound waves is preferably shorter than 3600 seconds. It is more preferably 1800 seconds or shorter. It is still more preferably 1500 seconds or shorter.
  • Delayed fracture due to resistance spot welding using welding electrodes may occur between 180 minutes and 720 minutes, with the start of current passage being 0 seconds. It is preferable to perform irradiation of sound waves before such delayed fracture occurs to suppress or eliminate the accumulation of hydrogen in the nugget, which is areas of tensile stress in the steel sheet. From this point of view, it is preferable to irradiate the nugget-equivalent surface with sound waves within 360 minutes from the start of current passage to the steel sheet. It is more preferably shorter than 180 minutes. It is still more preferably within 60 minutes. From the viewpoint of avoiding the risk of delayed fracture as much as possible, the time from the start of current passage to the start of sound wave irradiation is desirably as short as possible. Therefore, the lower limit of the time from the start of current passage to the start of sound wave irradiation is not particularly limited. However, considering the time required for the current passage itself, the lower limit of the above time is usually 10 seconds.
  • the amount of residual hydrogen in the nugget is preferably 0.5 ppm or less in mass fraction. It is more preferably 0.3 ppm or less in mass fraction. It may be 0 ppm in mass fraction. Because residual hydrogen in the nugget causes hydrogen embrittlement in a weld joint, the amount of residual hydrogen is desirably as low as possible. In general, resistance spot welding to a steel sheet with high strength is more likely to cause delayed fracture. However, in the present disclosure, sound waves are applied under predetermined conditions, so that the amount of residual hydrogen can be reduced satisfactorily even in the case of high strength steel sheets.
  • Irradiation of sound waves can use a common device (a sound wave irradiator or a sound wave generator) that generates sound waves and irradiates an object with the sound waves.
  • a sound wave irradiator examples include a sound wave transmitter, and a speaker equipped with a diaphragm or the like in a sound wave transmitter.
  • the installation method of the sound wave irradiator 7 is not particularly limited as long as the nugget is irradiated with the predetermined sound waves described above.
  • the sound wave irradiator 7 may be installed so that the direction of propagation of the sound waves is such that the sound waves hit at least one of the nugget-equivalent surfaces (reference signs 13 and 23 in FIG. 3 ) at the shortest linear distance.
  • the sound wave irradiator 7 may be installed so that the sound waves spread and propagate to reach and hit the nugget-equivalent surface even if the direction of propagation of the sound waves is not toward the shortest linear distance described above.
  • one sound wave irradiator 7 may be provided for each nugget-equivalent surface 13 or 23 , or one or more sound wave irradiators capable of irradiating all the plurality of nugget-equivalent surfaces on one surface with sound waves may be provided.
  • the sound wave irradiator 7 may be provided opposite to both surfaces 11 and 21 of the steel sheet.
  • nugget-equivalent surfaces on one surface it is acceptable to irradiate only one of the nugget-equivalent surfaces with sound waves, or irradiate any plurality of the nugget-equivalent surfaces with sound waves, or irradiate all the nugget-equivalent surfaces with sound waves, or irradiate the entire surface of the steel sheet.
  • the shortest linear distance between the surface of the steel sheet and the sound wave irradiator is preferably within 15 m. It is more preferably within 5 m.
  • residual hydrogen in the nugget can be reduced without heat treatment. Therefore, according to the present disclosure, it is possible to obtain a weld joint that exhibits excellent delayed fracture resistance while avoiding the risk that the chemical composition and/or microstructure of the steel sheet is changed from a desired state due to heat, compared to the conventional technique of performing heat treatment after welding. Further, the present disclosure does not require a heating device for coping with hydrogen embrittlement, which is advantageous in terms of working time and working cost.
  • the present disclosure which employs a simple method of sound wave irradiation without contacting the steel sheet, can be used particularly advantageously, for example, in resistance spot welding in automobile manufacturing that requires many detailed welding operations.
  • Two steel sheets of longitudinal direction: 150 mm ⁇ lateral direction: 50 mm ⁇ sheet thickness: 1.4 mm were used as a lower steel sheet 1 placed vertically downward and an upper steel sheet 2 placed vertically above the lower steel sheet 1 .
  • Table 1 lists the tensile strength of the lower steel sheet 1 and the upper steel sheet 2 , and the presence or absence of a coating on the surface and the overlapping surface of the steel sheet, which was either without coating (CR) or with coating (hot-dip galvanizing (GI), galvannealing (GA), coating weight was 50 g/m 2 per side).
  • the tensile strength was obtained by preparing a JIS No. 5 tensile test piece from each steel sheet along the direction perpendicular to the rolling direction and performing a tensile test in accordance with the provisions of JIS Z 2241 (2011).
  • a resistance spot welding point 6 schematically represents a welding trace formed on the surface of the steel sheet (weld joint) by the joining.
  • Both of the lower electrode 4 and the upper electrode 5 were chromium-copper DR-type electrodes having a diameter at the tip (tip diameter) of 6 mm and a curvature radius of 40 mm.
  • the electrode force applied during the joining was controlled by driving the lower electrode 4 and the upper electrode 5 with a servomotor, and a single-phase alternating current with a frequency of 50 Hz was supplied.
  • resistance spot welding points 6 were observed on the surfaces 11 and 21 of the lower steel sheet 1 and the upper steel sheet 2 after joining, as illustrated in FIG. 2 .
  • a nugget 3 which is schematically illustrated in FIG. 1 , was formed on the overlapping surfaces 12 and 22 of the lower steel sheet 1 and the upper steel sheet 2 along the thickness direction from the resistance spot welding point 6 .
  • Two weld joints were prepared under each set of current conditions to measure the amount of residual hydrogen in the nugget before and after sound wave irradiation, respectively.
  • the obtained weld joint was allowed to stand in the atmosphere at normal temperature (20° C.) for 24 hours, and whether or not delayed fracture occurred after the standing was visually judged. Further, when peeling and cracking of the nugget were not visually observed in the surface, a cross section in the thickness direction including the center of the nugget was observed with an optical microscopy ( ⁇ 50 times) to confirm the presence or absence of cracks in the cross section.
  • the amount of residual hydrogen in the nugget was measured by thermal desorption analysis.
  • a weld joint that had not been irradiated with sound waves was selected from the weld joints obtained under each set of current conditions, and a sample was obtained from the weld joint by cutting it into 1 cm ⁇ 1 cm ⁇ sheet thickness so that the resistance spot welding point was included in the center. After degreasing with ethanol, thermal desorption analysis was performed.
  • a weld joint that had been irradiated with sound waves was selected from the above weld joints, and a sample was obtained from the weld joint by cutting it into 1 cm ⁇ 1 cm ⁇ sheet thickness so that the resistance spot welding point was included in the center.
  • thermal desorption analysis was performed. The sample was heated at a heating rate of 200° C./hour, and the amount of hydrogen released from the sample was quantified by gas chromatography every 5 minutes to determine the hydrogen release rate (wt/min) at each temperature. The amount of hydrogen released was obtained by calculation by accumulating the obtained hydrogen release rates.
  • the value of part per million obtained by dividing the integrated value of the amount of hydrogen released up to 210° C. by the mass of the sample was defined as the amount (wt ⁇ ppm) of residual hydrogen in the nugget in mass fraction, and it is also listed in Table 1.
  • the resistance spot welding method of the present disclosure it is possible to satisfactorily avoid the problem of delayed fracture after joining steel sheets.
  • the method of manufacturing a weld joint of the present disclosure it is possible to easily obtain a weld joint that exhibits excellent delayed fracture resistance. Therefore, the present disclosure can be suitably used in the manufacturing process of automotive parts for automobiles and the like and in the assembly process of automotive bodies.

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JP2005103608A (ja) * 2003-09-30 2005-04-21 Nippon Steel Corp 高強度めっき鋼板をスポット溶接した継手の耐食性、引張強さおよび疲労強度向上方法
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JP6194765B2 (ja) 2013-11-08 2017-09-13 新日鐵住金株式会社 高強度鋼板のスポット溶接方法
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WO2022014173A1 (ja) 2022-01-20
MX2023000701A (es) 2023-02-13
EP4183510A4 (en) 2023-12-20
CN115803138A (zh) 2023-03-14
JP7184204B2 (ja) 2022-12-06
KR20230028488A (ko) 2023-02-28

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